In microwave and millimeter-wave harmonic generators, the desired harmonic is often produced by passing a sinusoidal signal through a non-linear device while tailoring the conduction angle of the non-linear device so as to maximize the level of the desired harmonic. A well-known relationship between harmonic amplitude and conduction angle is demonstrated in a classic Fourier series. The desired harmonic, once optimized, can then be isolated through filtration and amplification.
When high-order (fifth or greater) harmonics are to be obtained, this conduction-angle approach poses several problems. The allowable range of conduction angles decreases rapidly with high-order harmonics, requiring tighter and tighter conduction angles as the frequency rises. The difficulty of maintaining a tight conduction angle rises with the frequency. Normal variation in the requisite non-linear devices requires that each generator undergo tedious individual conduction angle adjustment in order to maximize the desired harmonic output. Such adjustments are incompatible with low cost, high volume production environments.
An additional problem arises in that such adjustments, once made, will vary as the non-linear components vary over time, requiring periodic calibration or re-adjustment.
For these reasons, high-frequency microwave and millimeter-wave harmonic generators are usually low-order multipliers (doublers, triplers, etc.) cascaded and combined to produce the desired frequency. This approach is not without its own problems. First, being a series of individual multipliers, such a harmonic generator requires more parts and more unique circuits than a single non-linear device harmonic generator, thus increasing cost while reducing reliability. Second, being composed of a plurality of cascaded multipliers, it is not possible to produce high-order prime-number harmonics (5.sup.th, 7.sup.th, 11.sup.th, 13.sup.th, 17.sup.th, etc.).
What is needed is a high-order harmonic generator wherein the conduction angle of a non-linear device is automatically controlled to maximize the output of the desired harmonic, thus eliminating the need for manual adjustment and compensating for both initial and temporal device variation .